The present invention relates to a thermal motor for converting thermal energy, such as solar energy, into mechanical motion. Heretofore, devices have been developed for converting thermal energy into mechanical energy, such as shown in U.S. Pat. No. 3,070,953 wherein a bi-metallic coiled spring member is subjected to hot and cold fluids alternately to expand and contract the spring member deriving reciprocating mechanical rotary motion therefrom. In U.S. Pat. No. 3,772,876 a reciprocating thermal motor is disclosed which also uses a bi-metallic spring element subjected to alternate hot and cold cycles with the source of heat being solar energy. However, much of the heat from the heated fluid is lost in such devices through contact with other parts of the motor other than the element which is to be heated. It can also be seen that such devices are fairly complicated, particularly the apparatus shown in U.S. Pat. No. 3,070,953.